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Whole house fan

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Is there a formula or calculation for the amount of vent opening needed out of the house/attic for a whole house fan? What is used as the basis as any unit that I have seen does not list any specs on a data plate, such as how much air they move per hour, etc.

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Hi,

It really depends on your climate and what your state's energy code says - if you have one - and that's a moving target. Our 2006 Energy code had specific requirements shown at the table on page 8-5 of the code (http://www.energy.wsu.edu/Documents/Bui ... e-2006.pdf) but the new 2010 code, which went into effect on January 1st, has been gutted of those requirements.

If any of you Washington State inspectors would like to download a copy of the 2010 Builder's Field Guide to the code, click here.

ONE TEAM - ONE FIGHT!!!

Mike

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This fan has been in the house a long time, decades likely. I saw very little attic ventilation, far less than common sense and what the GAF specs call for. I need a rough idea to educate the buyer, which I can estimate from the information provided.

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Use this formula, which is based on HVI-916 formula for NFVA

CFM=NFVA (square feet) x 2432 x square root(P)

where CFM= cubic feet per minute

NFVA= net free ventilation area (sq. feet)

P = pressure in inches of water column

subsituting in P=.05, which is a safe value for maximum attic pressure:

CFM=NFVA (square feet) x 2432 x square root(.05)

More details here: http://blog.airscapefans.com/archives/homepower-article

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